DE4033912C2 - Optical sensor - Google Patents

Description

The invention relates to an optical sensor with a integrates optical arrangement that includes a waveguide, optionally with a sensitive layer, and a this waveguide arranged diffraction grating for coupling of light in the waveguide, with changes in effective refractive index in the waveguide can be measured.

Such optical sensors based on diffraction gratings detect certain measuring substances, measure refractive indices of liquid media or show small mechanical shifts according to the effective refractive index of a waveguide being affected. This effective refractive index is determined using the Diffraction grating determined by the light in the waveguide is coupled in or out of the waveguide.

Sensors of this type are, for example, from WO 86/07149 known.  

The high accuracy of this sensor is based essentially insists that the coupling or decoupling of the light into the Waveguide or out of this waveguide with the help of Grid only possible under a very limited angular range is.

It is coupled into the waveguide with a Parallel beam. A measurement of the Light intensity can be made at the end of the waveguide. With a static arrangement with a fixed sensor head and is fixed light beam with respect to the angle of incidence the measuring range is very limited, since only in a small one Range of effective refractive indices and corresponding ones Coupling angle a signal can be measured at the detector.

Because the angle of incidence of the light beam into the diffraction grating must be very accurate (hundredths of a degree range) in order to Achieving coupling into the waveguide is a high one Mechanical storage effort interacting modules and also a high adjustment effort required.

It is also known to rotate or pivot the Provide sensor head so that a larger range of Coupling angles can be scanned. In this case but also precise mechanical adjustment elements in the Sensor head required.

Furthermore, one knows the coupling of a light beam on the Sensor head edge (end face coupling) and coupling out the grid. With this arrangement, however, the Manufacturing an additional processing step because of the necessary front surface polish required and also a very precise adjustment of the light source or one Coupling optics relative to the sensor head edge.

The "critical" coupling area is from the diffraction grating shifted to the sensor head edge, but also the  Point of radiation in the waveguide, the thickness dimension in Micrometer range, and the angle of incidence are correct and accordingly must be adjusted exactly.

Another disadvantage is that in the transition area between Light source or optics and the sensor head edge that Scattered light influencing the measurement result can occur.

From WO 88/10418 is an optical sensor with a integrated optical arrangement known with the chemical, biochemical or biological samples can be examined. The respective sample is in contact with the surface brought the integrated optical arrangement.

The integrated optical arrangement has one substrate and one wave-guiding film in which light is diffracted by a grating can be coupled into the waveguide. Changes in Properties of the waveguide under the influence of the examining sample are then analyzed.

The integrated optical arrangement is for this purpose under or irradiated with multiple angles of incidence and it will reflected, transmitted and / or propagating light then analyzed whether there was a particular Light incidence angle propagates a light wave or fashion.

WO 88/10418 are specific suggestions for the practical structure of the measuring arrangement and instructions for a simplified handling not to be removed. They are not practical Include suggestions to address the problem regarding the mechanical fine adjustment between the light source and the integrated optical arrangement to solve.

For different samples there is also a comparative one complex adjustment of the integrated optical arrangement required relative to the light source, which is particularly the case with Series measurements a particularly disadvantageous, considerable time and practical use with special needs.

The object of the present invention is a compact and simply design optical sensor to specify the Detection of different measured variables is suitable.

This task is accomplished with an optical sensor Features of claim 1 solved.

Because of the incoming, convergent light beam now no more complex adjustment required, since only it must be ensured that the "suitable" in the light beam Coupling light beam is included.

The angular position of the appropriate coupling light beam is determined based on the reflected light beam. Under the Angle for which the coupling conditions and thus the diffraction in part of the light is transmitted through the waveguide derived the waveguide. In this case, the reflected light beam at this angle a dark one Line whose location, e.g. B. evaluated with a diode row becomes.

The sensor head can now be replaced despite this occurring, unavoidable differences in location without any problems be carried out because the light beam so large and co-detecting the coupling light beam Angular range covers that even with different Sensor heads a measurement is possible. Now there are none Position readjustments required.

This is in series measurements where the sensor head is only for one single measurement is used, particularly advantageous. It this results in considerable time savings and a simplified one Service.

As sensitive layers, all come in thinner form Coatings of preparable substances in question, the one have sufficient optical transparency and their optical Determine properties by adsorbing a Change the substance to be detected. For example  different polymers or in polymers or siloxanes embedded organic functional groups can be used. Especially It is advantageous if as a sensitive layer or as Waveguide material from the substance class of Heteropolysiloxane (HPS) is provided, with targeted Selection of the sensitive layer from this substance class a particular substance component can be determined in each case. At Can use this class of substance for the sensitive layer special substances can be detected selectively. The sensitive layer such a substance is used in Wavelength range transparent and also homogeneous to Avoid wastage.

The invention is described below with reference to the drawing explained that an optical sensor with incident and shows reflected light.

An optical sensor designated as a whole by 1 has a sensor head 2 with a waveguide 4 located on a substrate 3 , which is designed here as a waveguiding film. The waveguide 4 also has a diffraction grating 5 through which light can be coupled into the waveguide 4 .

The sensor 1 also includes a light source 6 , focusing optics 7 and a measuring device 8 by means of which changes in the effective refractive index can be measured.

The effective refractive index is essentially dependent on the substrate 3 and the waveguide 4 , their refractive index and also the layer thicknesses being decisive.

The effective refractive index can be influenced by the addition of a measuring substance 9 to the waveguide 4 .

In order to be able to recognize such changes in the effective refractive index, essentially monochromatic light 10 is coupled into the waveguide 4 via the diffraction grating 5 .

Changes in the effective refractive index are noticeable both at the end of the waveguide 4 as changes in intensity and in the reflection region 11 through position shifts. In the optical sensor 1 according to the invention, an evaluation takes place in the reflection area 11 .

Coupling the light into or out of the waveguide 4 or out of it is possible with the aid of the diffraction grating 5 only in a very narrowly limited angular range. In the figure, the position of the appropriate coupling light beam 12 is shown by a dash-dotted line. Coupling into the waveguide 4 only takes place if this angular position relative to the diffraction grating is observed exactly. The coupling light beam 12 is also indicated by dash-dotted lines within this waveguide 4 .

In order to avoid complex mechanical adjustment devices for the exact setting of the coupling light beam 12 , a convergent coupling light beam 13 is present in the present sensor arrangement, which also covers the matching coupling light beam 12 . Accordingly, an exact adjustment of an individual coupling light beam 12 is no longer necessary, but an approximate and very uncritical alignment of the light beam 13 is sufficient here. Within this bundle of light rays 13 there are a large number of non-parallel light rays, which thus all shine in at a different angle at the diffraction grating 5 . Even when the light source 6 and sensor head 2 are shifted in position, no readjustment work is necessary, since the appropriate coupling light beam 12 is contained within the light beam 13 .

At the beam angle for which the coupling conditions and thus the diffraction in the waveguide 4 are fulfilled, part of the light is diverted through the waveguide 4 . In the reflection region 11 results in a dark line 14, is shown delineated for clarity in the figure by doppelpunktstrichlinierte lines at the reflection angle of the Einkoppellichtstrahles 12th Changes in the effective refractive index can be seen from the change in position of this dark line 14 , which serves as a pointer. Since here the position of the pointer formed by the dark line 14 and not the intensity is decisive, no reference signals are required to mask out fluctuations in brightness, or a reference intensity is automatically obtained by the bright area in the reflex, which is also included in each case.

A photodiode array can be provided as the measuring device 8 in the region of the reflected light beam 15 .

As already mentioned, the effective refractive index is changed by measuring substance 9 attached to the waveguiding film 4 . Accordingly, the dark line 14 within the diverging, reflected light beam 15 would also change.

In the figure, a sensitive layer 16 located on the waveguide 4 or the waveguiding film is indicated by dashed lines. This sensitive layer can preferably consist of a material of the substance class heteropolysiloxanes (HPS). Such an HPS layer changes its refractive index under the influence of the substance to be measured and thus also influences the effective refractive index.

It is particularly advantageous when using an HPS layer 16 that gas measurements can also be carried out. The HPS layer can also form the light-guiding layer 4 itself.

By specifically selecting the sensitive layer 16 or the waveguide 4 from the substance class of the heteropolysiloxanes, special substances can be detected selectively.

It should also be mentioned that when using an HPS layer, both Liquids as well as gases can be measured.  

It should also be mentioned that a plurality of measuring ranges can also be arranged next to one another on the substrate 3 . For example, different sensitive layers 16 could also be provided in the different areas, so that different substance components can be determined when examining a substance.

Claims (4)

1. Optical sensor ( 1 ) with an integrated optical arrangement ( 4 , 5 , 16 ) which has a waveguide ( 4 ), optionally with a sensitive layer ( 16 ), and a diffraction grating ( 5 ) arranged on this waveguide ( 4 ) Coupling of light into the waveguide ( 4 ), with changes in the effective refractive index in the waveguide ( 4 ) being measured, a convergent, essentially monochromatic coupling light beam ( 13 ) being present which contains the coupling light beam ( 5 ) that matches the diffraction grating ( 5 ). 12 ), whereby in the case of a light beam ( 15 ) reflected in the region of the diffraction grating ( 5 ), the exit angle of a dark line ( 14 ) forming a pointer can be determined by means of a measuring device ( 8 ), the integrated optical arrangement ( 4 , 5 , 16 ) as a sensor head ( 2 ) forms an interchangeable assembly of the sensor ( 1 ), with a Lich to form the convergent coupling light beam ( 13 ) t source ( 6 ) with at least one focusing optics ( 7 ) arranged in the beam path and wherein the measuring device ( 8 ) for the exit angle of the dark line ( 14 ) has one or more light detectors which emit a signal with respect to the exit angle. 2. Optical sensor according to claim 1, wherein the measuring device ( 8 ) has one or more photodiode arrays. 3. Optical sensor according to claim 1 or 2, wherein material from the substance class of the heteropolysiloxanes (HPS) is present as a sensitive layer ( 16 ) or as a waveguide ( 4 ), with a selective selection of the sensitive layer ( 16 ) from this substance class in each case certain substance component can be determined. 4. Optical sensor according to one of claims 1 to 3, wherein on the waveguide ( 4 ) a plurality of different sensitive layers ( 16 ) are present.